The present invention relates to a turbocharger.
Conventionally, turbochargers have been used, which utilizes kinetic energy of exhaust gas discharged by internal combustion engines to supercharge air to the engines. A typical turbocharger includes a turbine located in the exhaust system of an internal combustion engine and a compressor located in the intake system of the engine. When drawn into the turbine, exhaust gas discharged by the engine rotates the turbine impeller in the turbine. The turbine impeller is coupled to a compressor impeller located in the compressor. Thus, rotation of the turbine impeller rotates the compressor impeller. When the compressor impeller rotates, air drawn in through the compressor inlet is compressed and then delivered to the diffuser passage arranged outward of the compressor impeller. The air is subsequently delivered to a scroll passage. The supply of compressed from the compressor to the internal combustion engine improves the performance of the engine.
The compressor inlet is connected to the intake passage. Blow-by gas leaked from the internal combustion engine is drawn into the intake passage via a blow-by gas recirculation passage. Blow-by gas contains lubricating oil and fuel. The air drawn in by the compressor is compressed to become high-pressure compressed air. This increases the temperature of a wall surface that faces the diffuser passage, that is, the diffuser surface, through which the compressed air flows. Droplets containing oil as a main component are solidified at temperatures higher than or equal to, for example, 160° C. Thus, oil and the like are solidified and accumulated on the diffuser surface. Accumulation of oil and the like reduces the area of the diffuser passage, reducing the performance and operating characteristics of the turbocharger.
Japanese Patent No. 5359403 discloses a configuration in which a cooling passage is provided in the wall of a compressor housing member. Fluid that flows through the cooling passage cools the diffuser surface, thereby lowering the temperature of the diffuser surface. Accordingly, the temperature of the diffuser surface is kept lower than the temperature at which oil and the like are solidified. This limits solidification of oil and the like on the diffuser surface.
In the above described conventional configuration, when blow-by gas is drawn into the intake passage, water vapor in the blow-by gas freezes depending on the temperature of the air drawn into the compressor, and the ice may damage the compressor impeller. Japanese Laid-Open Patent Publication No. 2012-2192 discloses a configuration in which an intake passage has, for example, a heating passage such as a water jacket. Coolant for cooling the internal combustion engine flows through the heating passage. The temperature of the coolant is approximately 80° C., which is relatively high. Thus, the coolant flowing through the heating passage heats a part of the intake passage in the vicinity of the section for introducing blow-by gas. This limits freezing of water vapor in the vicinity of the blow-by gas introducing section. Therefore, damage to the compressor impeller by ice is limited.
Accordingly, there has been a demand for a configuration that effectively limit solidification of oil and the like contained in blow-by gas and freezing of water vaper contained in blow-by gas, without increasing the size of a turbocharger.